Since you are not going to return a value from your function, it probably
should be a Sub instead.
While the Temp variable method is probably the fastest, I thought the
readers of this thread might find a solution that does not require a
temporary variable of some interest.
If the two cells contain numerical values...
Sub Swap(C1 As Range, C2 As Range)
C1.Value = C1.Value + C2.Value
C2.Value = C1.Value - C2.Value
C1.Value = C1.Value - C2.Value
End Sub
If the two cells contain numerical and/or text values...
Sub Swap(C1 As Range, C2 As Range)
C1.Value = C1.Value & C2.Value
C2.Value = Replace(C1.Value, C2.Value, "")
C1.Value = Replace(C1.Value, C2.Value, "")
End Sub
Rick